In vitro bioassay of erythropoietin using synchronized rabbit erythroid precursors.

Synchronized erythroid precursors obtained from the bone marrow of rabbits and plated in methyl-cellulose were used as a bioassay for the measurement of erythropoietin (Ep). Rabbits were given five daily injections of phenylhydrazine followed by a single dose of actinomycin-D. This treatment resulted in a rapid repopulation of bone marrow by synchronized erythroid precursors which can be stored at -180 degrees C for long periods. Grown in vitro for 2 days in the presence of added Ep these cells divided to form colonies (CFUE). The erythroid nature of these colonies was confirmed by 59Fe incorporation into heme. Preliminary studies indicate that this system is suitable for the measurement of Ep in human sera. It is simple, inexpensive, reproducible, and permits measurements at the physiologic range of Ep concentrations.